SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Langston's Arco (former) : page 2 15615S. 7 1h Street, Lathrop CA. January 13, 2011 Since 1997, the groundwater gradient has changed from predominantly toward the south to northwesterly. , Due to this shift, the EHS was concerned that the elevated concentrations of dissolved TPHg in groundwater samples collected from well EW-1, located in the extreme southeast corner of the site, may have migrated across the site towards the unmonitored gap between MW-5 and MW-4. Data analysis shows MW-5 was previously impacted,by declining concentrations and is currently a 'non-detect' well. The EHD has concludedithat the dissolved plume is not migrating from DPE-2 to MW-5 or between MW-5 and MW-4. ' To enable the EHD to complete the closure evaluation of the site, please submit a report that includes or addresses the following concerns: • The completed site characterization in the context of a conceptual model. • A residual massestimate with calculations of the amount (pounds and gallons) of petroleum hydrocarbons still in place at the site. The risk to human health from residual soil and groundwater contamination at the site. (i.e.: soil gas/vapor intrusion potential to the people working in the building to the north of the site, to the family housing area to the west, direct contact to workers if the site is developed/improved, etc). The estimated time required for the site to achieve water quality objectives. In order to verify if the public is being exposed to petroleum impacted groundwater, the EHD directs you to collect groundwater samples from all water supply wells within 550 feet of the limits of the site's previous soil excavation and analyze them for TPHg, benzene, toluene, ethylbenzene, total xylenes (BTEX) and 1,2-dichloroethane (DCA). The data from the well sampling and your response to each of the above bulleted items is to be included in a No Further Action Request Report due on Geotracker by March - 11, 2011. Thank you for your. continued cooperation in investigating and evaluating your site. Please contact Michael Infurna at(209) 468-3454 if you have any questions. Michael J. Infurna Jr., REHS Nuel C. Henderson Jr., PG Senior Registered Environmental Health Specialist Engineering Geologist i c: Mr. James L. Barton, CVRWQCB, Underground Storage Tank Unit, 11020 Sun Center Drive #200, Rancho Cordova, CA 95670-6114 Mr. Mark Owens, SWRCB, Division of Clean Water Programs, Underground Storage Tank Program, PO Box 944212, Sacramento, CA 94244-2120 Mr. William Little, Advanced Geo Environmental Inc. (AGE), 837 Shaw Road, Stockton, CA 95215